3.4.2. Feeding site

Varroa mothers pierce the cuticle of honey bee
larvae and pupae on which they (Fig. 7a) and their offspring feed (Fig. 7b). In
late pupae, the wound can be seen under the binocular thanks to the scarring
process of the cuticle (Fig. 7c). It can
also be located by observation of the feeding mites, events that are relatively
rare and need an artificial in vitro
system to be observed (see section 3.2.2. ‘Breeding mites in the laboratory’).
In most cases, no wound can be seen on larvae or pupae and a staining method is
necessary to find it (Fig. 7d). The ability to locate the wound might be
necessary for behavioural studies of feeding behaviour or reproduction or for
secondary disease transmission studies (Kanbar and Engels, 2003). By extension,
this method can also be used for all cases in which a perforation of the cuticle
of immature honey bees has to be made visible (e.g. injection of pathogens or
hormones, Kanbar and Engels, 2005).

Kanbar and Engels (2004) designed a vital
staining method that allows the visualisation of feeding sites. They used
Trypan blue, a dye that enters damaged cells (Roche, 1999), i.e. cells around
the hole pierced by mother mites in the late 5th instar larvae, prepupae or
pupae cuticle. Feeding sites could thus be stained durably on live individuals
and observed over time (Herrmann et al.,
2005). Staining can be detected until the stage when the cuticle darkens to the
point of hiding the dyed blue cells. At this point the dyeing is not any longer
necessary.

Fig. 7. a. Adult varroa mite sucking haemolymph of a pupa at the feeding site. b.
varroa nymph sucking haemolymph of a pupa as the feeding site. c.
feeding site with melanisation (arrow). It is visible without staining. Such
instances are more frequent in older pupae. d. a feeding site (arrow)
on a white pupa after staining with Trypan blue. Photos: Swiss Bee Research
Institute.